/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.runtime.io.network.netty;

import org.apache.flink.shaded.netty4.io.netty.buffer.ByteBuf;
import org.apache.flink.shaded.netty4.io.netty.channel.ChannelHandlerContext;

import javax.annotation.Nullable;

import static org.apache.flink.runtime.io.network.netty.NettyMessage.BufferResponse;
import static org.apache.flink.runtime.io.network.netty.NettyMessage.BufferResponse.MESSAGE_HEADER_LENGTH;
import static org.apache.flink.util.Preconditions.checkNotNull;

/**
 * The decoder for {@link BufferResponse}.
 */
class BufferResponseDecoder extends NettyMessageDecoder {

	/** The Buffer allocator. */
	private final NetworkBufferAllocator allocator;

	/** The accumulation buffer of message header. */
	private ByteBuf messageHeaderBuffer;

	/**
	 * The BufferResponse message that has its message header decoded, but still
	 * not received all the bytes of the buffer part.
	 */
	@Nullable
	private BufferResponse bufferResponse;

	/** How many bytes have been received or discarded for the data buffer part. */
	private int decodedDataBufferSize;

	BufferResponseDecoder(NetworkBufferAllocator allocator) {
		this.allocator = checkNotNull(allocator);
	}

	@Override
	public void onChannelActive(ChannelHandlerContext ctx) {
		messageHeaderBuffer = ctx.alloc().directBuffer(MESSAGE_HEADER_LENGTH);
	}

	@Override
	public DecodingResult onChannelRead(ByteBuf data) throws Exception {
		if (bufferResponse == null) {
			decodeMessageHeader(data);
		}

		if (bufferResponse != null) {
			int remainingBufferSize = bufferResponse.bufferSize - decodedDataBufferSize;
			int actualBytesToDecode = Math.min(data.readableBytes(), remainingBufferSize);

			// For the case of data buffer really exists in BufferResponse now.
			if (actualBytesToDecode > 0) {
				// For the case of released input channel, the respective data buffer part would be
				// discarded from the received buffer.
				if (bufferResponse.getBuffer() == null) {
					data.readerIndex(data.readerIndex() + actualBytesToDecode);
				} else {
					bufferResponse.getBuffer().asByteBuf().writeBytes(data, actualBytesToDecode);
				}

				decodedDataBufferSize += actualBytesToDecode;
			}

			if (decodedDataBufferSize == bufferResponse.bufferSize) {
				BufferResponse result = bufferResponse;
				clearState();
				return DecodingResult.fullMessage(result);
			}
		}

		return DecodingResult.NOT_FINISHED;
	}

	private void decodeMessageHeader(ByteBuf data) {
		ByteBuf fullFrameHeaderBuf = ByteBufUtils.accumulate(
			messageHeaderBuffer,
			data,
			MESSAGE_HEADER_LENGTH,
			messageHeaderBuffer.readableBytes());
		if (fullFrameHeaderBuf != null) {
			bufferResponse = BufferResponse.readFrom(fullFrameHeaderBuf, allocator);
		}
	}

	private void clearState() {
		bufferResponse = null;
		decodedDataBufferSize = 0;

		messageHeaderBuffer.clear();
	}

	@Override
	public void close() {
		if (bufferResponse != null) {
			bufferResponse.releaseBuffer();
		}

		messageHeaderBuffer.release();
	}
}
